As a method of automatically setting an IP address of a node in a communication network conforming to IPV6 (Internet Protocol Version 6), there is a method of distributing an address using DHCPv6 (Dynamic Host Configuration Protocol version 6).
Methods of distributing an address using DHCPv6 includes a method in which a DHCP server or an upper router having a DHCP function uses RA (Router Advertisement) to distribute a prefix of an IP address to a router device (for example, see Patent Literature 1,2).
The router device to which a prefix is distributed redistributes the prefix to a node using RA, for example. The node communicates with the upper router using an IP address including the distributed prefix. For example, the upper router is connected to the Internet.